Apparatus having packet allocation function and packet allocation method

ABSTRACT

An allocation execution determiner finds a bias in flow bandwidths allocated to each of physical ports on the basis of a maximum flow bandwidth and an average flow bandwidth reflecting actual traffics, determines high and low in the flow bandwidths, and allocates traffics in such a manner that the traffics become averaged.

INCORPORATION BY REFERENCE

The present application claims priority from Japanese applicationJP2009-258497 filed on Nov. 12, 2009, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to apparatuses which has a function ofallocating packets using such a technique as to logically combining aplurality of physical lines connected between apparatuses and to treatthe physical lines as if they were a single line and packet allocationmethods used for the apparatuses, and more particularly, relates to anapparatus which has a function of distributing or allocating packets intwo steps of autonomously and beforehand avoiding a bandwidth overflowand effectively and suitably making the most of an excessive bandwidthin business fields of handling various sorts and types of traffics andalso to a packet allocation method used for the apparatus.

Due to spread Internet use, improved CPU performances of personalcomputers, and appearance of multimedia personal computers; delivery ofvoice and video signals is widely employed in addition to transfer oftext data in a packet transfer network. For the delivery of voice andvideo signals, it is required to suppress packet discard more severelythan the text data. Thus it is necessary to avoid such packet discard.

A prior art packet transfer apparatus employing such a technique as tocombining a plurality of physical ports into a logical port and treatingthe ports as the logical port, performs calculating operation on thebasis of information (e.g., MAC address, IP address, port number, andVLAN identifier) in packets, selects output one of the physical portsbased on the calculation result, and distributes the traffics to theselected output port.

However, there occurs a bias in the value of the calculation resultbased on the information within the packets. Thus when such packets aredistributed as they are, the traffics are concentrated on a specificport and therefore efficient packet transfer cannot be achieved, sinceflow bandwidths in the physical ports in the local port are notaveraged.

To avoid this, there is suggested a method of allocating nearly auniform bandwidth to a plurality of physical ports in a logical port asa link aggregation (refer to JP-A-2006-5437). The link aggregation is atechnique defined in IEEE802.1AX.

According to the method cited in JP-A-2006-5437, a data transferapparatus as a traffic distribution control apparatus allocates trafficsto a plurality of physical ports provided in a logical port as a linkaggregation. To this end, the data transfer apparatus calculates a hashvalue for a received packet using a hash function on the basis of atransmission destination address and a transmission originator addressof the received packet, and determines one of the physical ports as adestination. The data transfer apparatus includes a means forcalculating a flow ratio between the plurality of physical ports, and acontrol means for changing allocation of the number of hash values todetermine destination physical ports by feeding the calculated flowratio back to bandwidth distribution or allocation ratios between theplurality of physical ports.

In the apparatus disclosed in JP-A-2006-5437, when a logic specified fordetermining the destination physical ports is not suitable, a biasprobably occurs in the flow bandwidths allocated to the physical portsin the link aggregation. Even when such biased distribution orallocation is executed, it is not judged whether or not thedetermination is correct. At this time, a large quantity of packetsflow. And when the packet quantity exceeds a total of flow bandwidths inthe physical ports, this causes occurrence of a packet discard.

In order to solve the aforementioned problem, there are suggested a linkaggregation circuit which can automatically select allocation logicsaccording to a change in the property of a network and also a linkaggregation allocation method used for the link aggregation circuit(refer to JP-A-2008-166881).

According to the method disclosed in JP-A-2008-166881, the linkaggregation circuit using layer 2 for use of link aggregation has aplurality of ports for the link aggregation, a control means forautomatically optimizing a MAC allocation logic, and a means forallocating flow-in packets to a plurality of ports based on theoptimized MAC allocation logic.

However, the allocation logic optimizing method used in JP-A-2008-166881is allocation based on a MAC address, and allocation based on packet-ininformation other than the MAC address is not carried out.

In the prior art packet transfer apparatus using such a technique as tocombine a plurality of physical ports into a logical port and to handlethe physical ports as the logical port, when flow bandwidths becomeunbalanced more or less or when a suitable packet distribution orallocation logic is not specified, a bias occurs in the flow bandwidthsallocated to the physical ports. Under such a condition, when a largequantity of packets flows and the packet quantity exceeds a total offlow bandwidths of the physical ports, even presence of an excessivebandwidth in the other logically-combined physical ports will causeoccurrence of a packet discard.

In recent years, an administrator or operator monitors flow bandwidthsat all times, and when a bandwidth overflow is predicted, the operatormanually adds a new line and changes output ports for packet flow. Thismay probably involve an error caused by the manual operation wheneverthe change is carried out.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a technique forcombining a plurality of physical ports into a single logical port andhandling the physical ports as if the physical ports were a singlelogical line, wherein, when it is desired to select output ones of thephysical ports on the basis of any identifier in packets and to transferpackets to the selected physical ports, packet allocation isautonomously carried out in two steps while reflecting actual traffics,thus solving the aforementioned two problems. In this way, sinceaveraged packets as a whole are made to flow, an excessive bandwidth iseffectively used, thus avoiding a packet discard.

In accordance with an aspect of the present invention, there is provideda network transfer apparatus which includes a bandwidth monitor formonitoring traffics for each of physical ports of the network transferapparatus combined into a logical port; a allocation executiondeterminer for determining whether or not the monitored traffics exceedsa predetermined threshold for the bandwidths of the physical ports; adivision executor for again allocating the traffics of the physicalports in the logical port; and a allocation result determiner fordetermining whether or not the traffics of the physical ports after theallocation by the division executor is smaller than the predeterminedthreshold.

In the network transfer apparatus, the allocation execution determinerdetermines whether or not the monitored traffics is larger than thepredetermined threshold. When the monitored traffics is larger than thepredetermined threshold, the division executor allocates the monitoredtraffics. When the allocation result determiner determines that thetraffics of the physical ports after the allocation exceeds thepredetermined threshold, the division executor again allocates thetraffics.

In the aspect of the invention, when a bias occurs in flow bandwidthsallocated to the physical ports of the logical port and a total maximumof the flow bandwidths of the physical ports exceeds a thresholdspecified by an administrator or operator, the operator divides themagnitudes of the flow bandwidths according to a previously specifiedthreshold, one of the traffics having a larger flow bandwidth isextracted and allocated to obtain averaged distribution or allocation,and thereafter, the remaining traffics are allocated. As a result, thetraffics are averaged as a whole and such packet allocation as toprevent packet discard can be autonomously achieved. Thus the bandwidthsof all the physical ports in the logical port can be effectivelyutilized while eliminating the need for the operator to always monitorthe flow bandwidths.

Since packet allocation can be autonomously optimized in the presentinvention, the need for the operator to manually optimize it whenever abias occurs in the flow bandwidths allocated to the physical ports canbe eliminated, and an error involved by the manual optimization can beprevented. Thus such a highly reliable service as to stop communicationstoppage caused by the changing operation or erroneous operation can beprovided.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary arrangement of networks towhich a packet transfer apparatus in accordance with an embodiment ofthe present invention is applied;

FIG. 2 shows an example of a statistical table in a packet transferapparatus as a prior art;

FIG. 3 is a block diagram of an arrangement of a packet transferapparatus in accordance with the embodiment of the invention;

FIG. 4 shows an example of a timer held in a memory in FIG. 3;

FIG. 5 shows an example of a data structure of the memory of FIG. 3;

FIG. 6 is a flow chart for explaining operations of a allocationexecution determiner and a allocation result determiner in FIG. 3;

FIG. 7 shows an example of a data structure of an allocation counterstorage in FIG. 3;

FIG. 8 shows a structure of a logical port for packet transfer when abias is generated in the embodiment of the invention;

FIG. 9 shows an example of a division method memory table havingdivision methods recorded therein to be executed by an allocator in FIG.3; and

FIG. 10 shows an arrangement of the logical port for packet transferafter the allocation execution of the embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be briefly explained. As first one of features of theinvention, a packet transfer apparatus of the invention using a logicalport obtained by combining a plurality of physical ports as in a linkaggregation is featured in that, when a bias occurs in traffics for eachof the physical ports of the logical port, the apparatus again dividesor allocates the traffics to correct the bias.

As second one of the features, since traffics flow through the logicalport of a virtual LAN called a VLAN, the apparatus monitors traffics foreach VLAN and divides or allocates the traffics into the respectivephysical ports.

Third one of the features will be explained. Many VLANs may beaccommodated within each logical port. Thus, at this time, upon trafficre-allocation, re-allocation of all the VLANs to the respective physicalports causes a large load to be applied to the packet transferapparatus. To avoid this, the load of the entire apparatus is reduced byapplying the re-allocation only to physical ports having large trafficaverage flow bandwidths, in particular, in a predetermined time. Theaverage flow bandwidth used in the explanation of the present inventionmeans an amount of an average traffic data flow in a certain constanttime. For example, assume that a VLAN has an average flow bandwidth of600 Mbps. Then this means that data of average 600 Mbit per second flowsin the VLAN (or the VLAN has such an amount of traffic).

Fourth one of the features is that the apparatus confirms whether or nottraffics of each physical port after allocation are smaller than apredetermined threshold. When the traffics are larger than thepredetermined threshold, the apparatus performs its trafficre-allocation. This means that traffic allocation based on apredetermined algorithm or the like is not always evenly carried out,and thus a determining process is provided after the allocation.

Explanation will be made as to an embodiment of the present invention byreferring to the accompanying drawings. FIG. 1 is a block diagram of aconfiguration of networks to which a two-step packet allocation methodof the present invention is applied.

A packet transfer apparatus 1 or 2 may employ a technique for virtuallycombining a plurality of physical lines connected with adjacentapparatuses into a logical line and handling the physical lines as ifthe physical lines were a single line such as link aggregation. In thiscase, parallel communication is carried out with the adjacentapparatuses and a total of bandwidths of the combined physical ports canbe used. When a trouble takes place in any of the plurality of physicallines, the communication can be continued using the other lines.Accordingly, bandwidth expansion with the adjacent apparatuses andredundancy can be secured.

FIG. 3 is a block diagram of an arrangement of a packet transferapparatus which employs the two-step packet allocation method of thepresent invention. In FIG. 3, a packet transfer apparatus 3 includes apacket receiver 301, an output port allocator 302, a packet transferer303, packet transmitters 304, 305, 306, a flow bandwidth storage 307, abandwidth monitor 308, a memory 309, a allocation execution determiner310, an allocator 311, a allocation counter storage 312, and aallocation result determiner 313.

The plurality of packet transmitters 304, 305, 306 are combined into asingle logical line as a logical port. However, a combination ofcombining physical ports may be made not only for ports within the samepacket allocation apparatus but also for ports extended within adjacentapparatuses.

The packet receiver 301, when receiving a packet, stores the receivedport therein and passes the packet to the output port allocator 302. Theoutput port allocator 302 reads an identifier allocated to each VLAN,performs calculation on the basis of configuration and statusinformation set in the packet transfer apparatus and information onports not receiving the packet within the same VLAN, allocates thepacket to an optimum port, and then passes the packet to the packettransferer 303 in such a manner that any of the packet transmitters 304,305, 306 transmits the packet. The flow bandwidth storage 307 alwaysmonitors the flow bandwidth of the output port when the packet istransmitted and stores the monitored information, for example, in such aform as shown in FIG. 2. FIG. 2 shows an individual logical-port-No datatransmission/reception statistical table having information about a VLANidentifier, an output port, transmission packets count, a discardpackets count recorded therein. Such information may be stored in theflow bandwidth storage 307 or may be stored in the respective bandwidthmonitors of apparatuses. Information of FIG. 2 is used for preparingsuch a table of FIG. 5 as to be explained later.

The apparatus of FIG. 3 is arranged so that, in order to obtain a hightransfer performance, the apparatus performs calculation and portallocation and then transfers the packet to the associated port.However, the apparatus may be arranged so that the apparatus transfersthe packet to a port not receiving any packet and then performscalculation then transfers the packet from the output port.

Although transmission packet allocation is carried out for eachidentifier allocated to each VLAN, the allocation may be carried outwith use of any of information (such as MAC address, IP address and portnumber) within the packet.

The bandwidth monitor 308 refers to information in the flow bandwidthstorage 307; calculates, at intervals of a constant time, a maximum flowbandwidth, an average flow bandwidth, and a total bandwidth for eachidentifier and output port within the packet associated with a logicalport number upon transmission; and stores its calculation result in thememory 309. In this connection, “constant time” at the intervals isassumed to be a momentary time unit for the maximum flow bandwidth andbe a sufficient time unit for the average flow bandwidth, and berearranged in a descending order of average flow bandwidth each time theaverage flow bandwidth is updated. The rearranged data will be detailedlater.

FIG. 4 shows an example of timing when timer 401 held in the memory 309updates the maximum flow bandwidth and the average flow bandwidth. Forexample, the timer stores information when the bandwidth monitor 308refers to the flow bandwidth storage 307 at intervals of 2 seconds, andcalculates a average flow bandwidth and a total flow bandwidth atintervals of 168 hours. When a variation occurs in the calculationresult, the timer rearranges such flow bandwidths in a descending orderof average flow bandwidth and perform updating operation. Calculation ofthe maximum flow bandwidth and the total maximum flow bandwidth iscarried out at timing point of detecting the maximum flow bandwidthduring the referring operation. In this connection, the timer 401 may beimplemented in the form of a program stored in the memory or in the formof hardware.

The allocation execution determiner 310 monitors information in thememory 309 at all times and determines whether or not to executeallocation. The allocator 311 allocates traffics of a VLAN having a highaverage flow bandwidth by such a method of allocating traffics accordingto a allocation counter value.

As a method of selecting VLANs having high average flow bandwidths, oneof VLANs having one of the high average flow bandwidths numbered by apredetermined number from the highest average flow bandwidth may beselected, or upper ones of the VLANs having flow bandwidths which occupyseveral percentages or more of the total flow bandwidth of the logicalport may be selected. Other selecting means may be allowed, as a matterof course.

Allocation result determiner 313 refers to information in the memory 309and determines whether or not the allocated result is correct. When itis determined that the allocated result is correct, the output portallocator 302 calculates the remaining traffics and allocates them to anoptimum port. When it is determined that the allocated result is notcorrect, “1” is added to the allocation counter value and the allocator311 again performs allocation according to the allocation counter value.

Explanation will next be made as to the data structure of the memory309. FIG. 5 shows an example of a data structure of the memory 309. InFIG. 5, the memory 309 includes two types of tables, that is, anindividual logical-port-number table (table 501) having a maximum flowbandwidth, a maximum flow bandwidth, and a total average flow bandwidthfor each VLAN identifier and each output port, calculated by thebandwidth monitor 308 and associated with a logical port number; and anindividual port total table (table 502) having a total maximum flowbandwidth and a total average flow bandwidth for each output port.

The tables 501, 502 of FIG. 5 are prepared on the basis of informationof the individual logical-port-No data transmission/receptionstatistical table of FIG. 2. In this connection, although the outputport is determined in units of VLAN identifier in the presentembodiment, the output port may be determined in units of IP address,MAC address or the like.

The table 501 has an logical port number, a VLAN identifier, an outputport number, a maximum flow bandwidth, an average flow bandwidth, atotal maximum flow bandwidth and a total average flow bandwidth for eachlogical port. In the present embodiment, the logical port number is setat “1”, the output port number is set at “1” for a traffic when the VLANidentifier is “32”, the maximum flow bandwidth is set at 350 Mbps, andthe average flow bandwidth is set at 200 Mbps.

The table 502 has a total maximum flow bandwidth and a total averageflow bandwidth associated with an output port number.

Rearrangement of the average flow bandwidths and calculation of themaximum flow bandwidth and the total maximum flow bandwidth with use ofthe timer of FIG. 4 are carried out by updating data of the table 501.More specifically, in the table 501, data are sorted in a descendingorder of average flow bandwidths for each of VLANs belonging to the samelogical port. In FIG. 5, for example, when attention is directed to arecord of a logical port number “1”, it will be seen from the drawingthat data are sorted in an order of average flow bandwidth such as“200”, “80” and “30”, that is, in a descending order. The same holdstrue even for another logical port.

Explanation will then be made as to the operation of the two-step packetallocation method. FIG. 6 is a flow chart for explaining the operationsof the allocation execution determiner 310 and the allocation resultdeterminer 313 in FIG. 3.

The allocation execution determiner 310 monitors information in thememory 309 at all times, and confirms whether or not a total maximumflow bandwidth in a packet output physical port exceeds a specificthreshold previously set by the operator (step 601). When the totalmaximum flow bandwidth exceeds the specific threshold, the allocationexecution determiner goes to a step 602. When the total maximum flowbandwidth does not exceed the specific threshold, the allocationexecution determiner determines that allocation execution is unnecessaryand terminates its processing operation.

The allocation execution determiner 310 confirms whether or not thetotal average flow bandwidth within the logical port exceeds thespecific threshold previously set by the operator on the basis of theinformation of the memory 309 (step 602). In the present embodiment, theallocation execution determiner refers to the individuallogical-port-number table 501 and confirms the value of the maximum flowbandwidth of “620 Mbps” for the logical port number of “total 1”. Whenthe total average flow bandwidth does not exceed the specific threshold,the allocation execution determiner goes to the next step 603. When thetotal average flow bandwidth exceeds the specific threshold, theallocation execution determiner determines the allocation execution isimpossible and outputs an alarm (step 608).

The allocation execution determiner 310 confirms whether or not aconstant time interval previously set by the operator from theprevious-time allocation execution is idle (step 603). When the constanttime interval is idle, the allocation execution determiner goes to anallocating step 609. When the constant time interval is not idle, theallocation execution determiner determines that the allocation executionis impossible and outputs an alarm (step 608). In this connection, the“constant time interval” is set at such a time as not overlapped withthe information updating or rearrangement of the bandwidth monitor 308.

This is because, when the allocation frequently occurs in the constanttime interval, this means that the transfer performance of the packettransfer apparatus cannot follow up the traffic and this may be requiredto add on its facilities. In such a condition, the frequent allocatingoperation results not only in no improvement of traffic bias but also inunstable traffic, possibly leading to generation of a packet loss. Thetime interval is considered to be set, for example, at 3 or 6 months.

The allocation result determiner 313 confirms on the basis of theinformation of the memory 309 whether or not a result allocated in theallocator 311 is correct (step 604).

The correct determining method means the a total maximum flow bandwidthis calculated for each of output ports newly allocated with use of theVLAN identifier and the maximum flow bandwidth of the output port andits calculation result does not exceed a specific threshold of thephysical port bandwidth previously set by the operator. In the presentembodiment, the allocation result determiner refers to the individualport total table 502 and confirms the value of the maximum flowbandwidth of “350 Mbps” for the output port number of “1”. Determinationas correct causes the allocation result determiner to go to a step 605and writes “0” in the allocation counter for initialization (step 610).Determination as not correct causes the allocation result determiner toadd “1” in the allocation counter (step 606) and to go to a step 607.

The allocation result determiner 313 confirms whether or not tocontinuously execute the allocation (step 607). When the count of theallocation counter is smaller than “8”, the allocation result determineragain goes to an allocating step 609 because the allocation execution isvalid. When the allocation counter is at “8”, the allocation resultdeterminer determines that the allocation execution is impossible andoutputs an alarm (step 608).

Explanation will next be made as to the data structure of the allocationcounter storage 312. FIG. 7 shows an example of the data structure ofthe allocation counter storage 312. In FIG. 7, the allocation counterstorage 312 has a logical port number and an allocation counter (table701). The logical port number is read and recorded as the number of thelogical port determined by the allocation execution determiner 310 toexecute the allocation. The allocation counter has a value of theallocation counter which is associated with the logical port number andwhich is used to determine an allocating method to be executed by theallocator 311. The allocation counter has an initial value of “0”, andthe value of the counter is added by “1” and when the allocation resultdeterminer 313 determines that the allocating method after theallocation is not correct, the value is written in the counter value.

The allocating method of the allocator 311 will be explained. FIG. 8shows an arrangement of one logical port when a bias occurs in theallocation before the present invention is applied. FIG. 9 shows anexample of the data structure when an allocating method to be executedby the allocator 311 is stored therein. This data may be stored in thememory 309. In the present embodiment, when traffics flow throughphysical ports 1, 2, 3, 4 (801, 802, 803, 804), a result after theallocating method set in the allocator 311 is applied to 15 of thetraffics numbered sequentially from number “1” in a descending order ofaverage flow bandwidths held in the memory 309 is shown in an allocatingmethod 901.

Assume that one of physical ports in a logical port has a smallestnumber x and another of the physical ports has a largest number y. Thatis, assume in the present invention that the port 1 is x and the port 4is y. In the allocating method 901, in the case of the allocationcounter “0”, traffic allocation starts with the port x and ends in theport y, and allocation is repetitively made to the ports one by onesequentially toward a larger port number.

In the allocating method 901, in the case of the allocation counter “1”,traffic allocation starts with the port x and ends in the port y,traffic allocation is repetitively made to the ports one by onesequentially toward a larger port number. In the second round,thereafter, traffic allocation starts with the port y and ends in theport x and allocation is made to the ports one by one sequentiallytoward a smaller port number. Such a sequence is repeated.

In the allocating method 901, in the case of the allocation counter “2”,traffic allocation starts with the port x and ends in the port y andallocation is made to the ports one by one sequentially toward a largerport number in the first round. In the second and subsequent rounds,traffic allocation starts with the port (x+1), (x+2), . . . , (y−1), andy and ends in the port x, (x+1), . . . , (y−2), and (y−1) and trafficallocation is made to the ports one by one sequentially a larger portnumber, in the respective rounds. At this stage, the allocation returnsto the port x and allocation is made one by one to the last port. Such astep is repeated.

In the allocating method 901, in the case of the allocation counter “3”,traffic allocation starts with the port x and ends in the port y, andthe allocation is made to the ports on every two basis sequentiallytoward a larger port number. Such a step is repeated.

In the allocating method 901, in the case of the allocation counter “4”,traffic allocation starts with the port x and ends in the port (y−1),and the allocation is made to the ports one by one sequentially toward alarger port number. Thereafter, in order to put a bias to the port y,two traffics are allocated to the port y. Such a step is repeated.

In the allocating method 901, in the cases of the allocation counters“5”, “6” and “7”, the bias of the allocation counter “4” is put to theports (y−1), (y−2) and (y−3) respectively and the allocation is made ina similar manner to the above.

FIG. 10 shows an arrangement of one logical port when the presentinvention is applied to FIG. 8. In the present embodiment, the result ofFIG. 10 shows that packets are uniformly allocated to the ports 1, 2, 3and 4 in an averaged manner as a whole.

In this way, in the present embodiment, flow bandwidths for actualtraffics are reflected. Thus, when a bias takes place in the flowbandwidths allocated to physical ports of a logical port, there is foundsuch a physical port that packets overflow, and the invention apparatusdetermines the necessity of reallocation of the packets; the apparatusallocates the packets in such a manner that traffics having large flowbandwidths are averagedly allocated. As a result, packet allocationaveraged as a whole can be autonomously achieved, and the bandwidth ofall the physical ports of the logical port can be effectively utilized,thus avoiding packet discard.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

The invention claimed:
 1. A network transfer apparatus comprising: abandwidth monitor for monitoring traffics for each of physical ports ofthe network transfer apparatus combined into a logical port; anallocation execution determiner for determining whether or not themonitored traffics exceeds a predetermined threshold for the bandwidthsof the physical ports; a division executor for again allocating thetraffics of the physical ports in the logical port; and an allocationresult determiner for determining whether or not the traffics of each ofthe physical ports after allocated by the division executor, is smallerthan the predetermined threshold, wherein the allocation executiondeterminer determines whether or not the monitored traffics is largerthan the predetermined threshold in such a manner that, when themonitored traffics is larger than the predetermined threshold, thedivision executor allocates the monitored traffics, and when theallocation result determiner determines that the traffics of thephysical ports after the allocation exceeds the predetermined threshold,the division executor again allocates the traffics; wherein a pluralityof VLANs are accommodated in the logical port, and allocation oftraffics of the physical ports in the logical port is made for each ofhe VLANs; wherein ones of the traffics of the physical ports in thelogical port which have bandwidth flows of a constant or more valuesselected based on a predetermined judgment criterion, are allocated; andwherein the predetermined judgment criterion specifies that averagebandwidth flows of the traffics are sequentially added together in adescending order of bandwidth flows and when a sum of the averagebandwidth flows exceeds a constant percentage of a sum of the bandwidthflows of the traffics flowing through the logical port, the traffics areselected as an allocation target.
 2. An network transfer apparatusaccording to claim 1, wherein the predetermined judgment criterionspecifies that only a predetermined number of ones of the traffics in adescending order of bandwidth flows are selected as an allocationtarget.
 3. A network transfer apparatus according to claim 1, whereinthe apparatus includes a memory for storing therein a first identifierfor uniquely identifying the logical port, a second identifier foruniquely identifying the traffic, a third identifier of the physicalport allocated to the traffic, and an average flow of the trafficassociated with the first and second identifiers, and wherein theapparatus performs allocating operation over the traffics of thephysical ports in the logical port by referring to the memory.
 4. Anetwork transfer method comprising: monitoring traffics of each of aplurality of physical ports in the network transfer apparatus in alogical port obtained by logically combining the physical ports;determining whether or not the monitored traffics exceed a predeterminedthreshold for a bandwidth of the physical ports; again allocating thetraffics of the physical ports in the logical port; and determiningwhether or not the traffics of the physical port after allocation of thedivision executor, is smaller than the predetermined threshold, whereinit is determined whether or not the monitored traffics exceed thepredetermined threshold, and when the monitored traffics exceed thepredetermined threshold, the monitored traffics are allocated, and whenit is determined that the traffics of the physical port after theallocation exceeds the predetermined threshold, reallocation is carriedout; wherein a plurality of VLANs are accommodated in the logical port,and allocation of the traffics of the physical ports in the logical portis carried out on each VLAN basis; wherein ones of the traffics of thephysical ports in the logical port which have bandwidth flows of aconstant or more values selected based on a predetermined judgmentcriterion are allocated; and wherein the predetermined judgmentcriterion specifies that average bandwidth flows of the traffics aresequentially added together in a descending order of bandwidth flows andwhen a sum of the average bandwidth flows exceeds a constant percentageof a sum of the bandwidth flows of the traffics flowing through thelogical port, the traffics are selected as an allocation target.
 5. Anetwork transfer method according to claim 4, wherein the predeterminedjudgment criterion specifies that only a predetermined number of ones ofthe traffics in a descending order of bandwidth flows are selected as anallocation target.
 6. A network transfer method according to claim 4,wherein the system further includes a memory for storing therein a firstidentifier for uniquely identifying the logical port, a secondidentifier for uniquely identifying the traffic, a third identifier ofthe physical port allocated to the traffic, and an average flow of thetraffic associated with the first and second identifiers, and whereinthe system performs allocating operation over the traffics of thephysical ports in the logical port by referring to the memoryinformation.